Multioffice telephone system



March 14, 1.933. J. wlcKs MULTIOFICE TELEPHONE SYSTEM Origal Filed Sept. 28. 1929 9 Sheets-Sheet 1 a s N NSR xmbm J. WICKS MULTIOFFICE TELEPHNE SYSTEM March 14, 1933.

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March 14, 1933. 1 WICKS 1,901,068

MULTIOFFIE TELEPHONE SYSTEM Original Filed Sept. 28, 1929 9 Sheets-Sheet 4 March 14, 1933. J. w'lcKs MULTICFFIGE TELEPHONE SYSTEM.

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Jn hn Minka March 14, 1933 l W|CK5 1,901,068 2 v `l/IULTIOFFIICE: TELEPHONE SYSTEM origina; Filed sept. 29, 1929 9 sheetsfsheet 6 D/FFEPENT/AL Jahn Winks March 14, 1933.

J. WlcKs MULTIOFFICE TELEPHONE SYSTEM 9 Sheets-Sheetl '7 Original Filed Sept. 28, 1929A Ellh 14, WICKS MULTIOFFICE TELEPHONE SYSTEM original Filed sepi. 28, 1929 9 Shee 11s-Sheet 8 @mum d2.

mi b5 March 14, 1933. Jj wlcKs MULTIOFFICE TELEPHONE SYSTEM 9 Sheets-Sheet 9 Original Filed Sept. 28. 1929 mmm patented ar. 14, 1933 Lamas MT1-:NT4 OFFICE JOHN WICKS, 0F OAK PARK, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO ASSO- A OF CHICAGO, ILLINOIS, A CORPORATION OF CIATED .ELECTRIC LABORATORIES, INC. DELAWARE MLTIOFFICE TELEPHONE SYSTEM Application led September 28, 1929, Serial No. 895,882. Renewed March 2B, 1932.`

This invention relates to multi-ofiice telephone .systems in general but is concerned more particularly with multi-office automatic telephone systems of the so called fmverted type, in which talking and holding current is supplied from the first selector instead of vfrom the connector. A system of .this type is shown in the copending application of J. Wicks` Serial No. 297,611. filed August 6, 1928, nowvljatenbNo. 1,778,204, Oct. 14, 1930, of which this lnvention may be considered as an improvement.

The invention has for its broad objects the provision of new and improved C11-cuits and switches for use in systems of the above type, for making such systems more eiiicient and practical, and for providing additional service features.

One feature of the invention is a tandem toll service trunking arrangement in which two-wav inter-oiice trunks are utilized for both lobal and toll service. This arrangement, incidently, requires'new combination local and toll selectors and connectors whlch also form a part of the invention. The trunks connecting the toll board and the tandem oice are likewise for two-Way traffic and serve both as toll completing and toll recording trunks. v In addition, the. system is arranged for preferred toll service, 1. e. toll calls may be completed to lines engage-d in local connections.

Another feature of the invention is the revertive ringing arrangement. This permits the subscriber to signal an extension station on the same line as is done in party line systems. The revertive ringing apparatus is also useful for testing and adjust-ing .substation ringers, permitting this to be done by a repair man at the sub-station Without any assistance from the central olice.V

Another feature is the arrangement for transmitting alarm signals from an unattended exchange to an operator over the regular inter-ofiiceand toll'board trunks. Theof the exchanges and is available for local or toll calls.

The foregoing features together .Vith others not specifically mentioned, will be described in detail hereinafter, reference beingvhad to the accompanying drawings.

or the purpose of this description, it has been vchosen to show the application of the inventlon in a telephone system comprisin two automatic offices and a manual toll o tice. It' is to be understood,.however, that the use of the invention is not limited toV In the system used for illustration, the allto-` matic oilices are of the one-thousand Iline type, although it is obvious that oiices of any other size may be employed. In order to provide a universal numberin system the numbering is on a four digit basis and the local first selectors are arranged to cancel the first digit on local calls. It is further assumed that the two automatic offices are normally unattended and provision is made f for extending alarm signals from these offices to the toll board over the regular service trunks. The alarm from each oflice takes a different route to the operator who is thus advised of the particular oice in which ,the alarm originates.

Referring now to the accompanying drawings comprising Figs. 1 to 10, inclusive, Figs. 1 to 9, inclusive, show by means of the usual circuit diagrams a sufficient amount of equipment in a telephone system employing the invention, to permit the invention to be readily described and understood. Fig. 10 is a layout diagram showing the manner with which the sheets of drawin s should be arranged in order to show the lnterrelation of the various circuits.

In Fig. 1 is shown a subscribers line serving sub-stationT and extension station T1 and terminating in rotary line switch LS. The sub-stations are of the usual automatic type. The line switch LS is of the well known rotary type, having no normal or home osition, and is provided with an extra wiper or metering purposes. The line switch has access to local first selectors of which one selector SR is shown. Selector SR mechanically is an ordinary twomotion Strowger type switch. The circuit of this selector is of the type required in the inverted system and the switch is arranged to supply battery .for the control loop as well as talking battery for both the calling and called subscribers. Selector SR has access by way of its wipers and banks to local connectors, reverting ringingrelay groups vtrunks leading to the toll board, and trun s extending to the other automat-ic exchanges of the system, such as trunks to the exchange B, The line switch n and selector in Fig. 1 are in exchange A.

Fig. 2 shows a revertive ringing relay group RC accessible to local first selectors of the automatic exchange A. This relay group is arranged to ring back on the calling line, to signal the extension station on that line.

Tn Fig. 3 is shown a combination local and toll connector C and the sub-station T2 terminating a subscribers line. Mechanically the connector is a Strowger type, vertical and rotary switch similar to selector SR of Fig. 1. The circuit, however, is arranged to operate in an inverted system with selectors such as selector SR.

F ig.4 shows a trunk relay group RCT terminating a combined recording and completing trunk connecting the toll board and oftice A. The dialling cord DC is used for extending calls over these trunks to the automatic exchange. #Incoming calls are answered by means` of the usual operatorp answering cord ACV of which only a part is shown. Toll calls are also completed by the answering cord or by a regular toll cord (not shown).

Fig. 5 shows a toll transmission selector TTS in which the trunks from the toll board terminate at the automatic exchange. This switch is also of the usual Strowger, vertical and rotary type and mechanically is very similar to selector SR. A special feature ot this switch is the arrangement for switching through on tandem toll calls as will be explained in later paragraphs. The switch teeds holding battery and talking current for the called su scriber and the operator in the same manner as local selector Slt.

In Fig. 6 is shown an incoming selector repeater ISR terminating a two way trunk connecting two automatic oilices. ltflechanically, this switch is similar to selector SR. The circuit, however, is modified to adapt it for trunk service.

Fig. 7 shows an alarmsigrial relay group ASR for transmitting alarm signals indicatmg unstandard conditions in the automatic exchanges tothe toll operator. This relay group actually comprises two distinct operating elements. One of these elements is associated with an inter-oiice trunk such as the trunk terminating in selector TSR of Fig. 6 and operates to relay alarm signals over this y trunk, to the toll operator by way of a toll understanding of the operation of the ap-l paratus. lt may be noted here that the ob- ]ect 1n classifymg the alarm signals as is done in this instance' is to give the operator an, idea of the seriousness of the trouble in the automatic exchange. Certain unstandard conditions will tie up only a single piece of apparatus, and thus not etlect the services of the exchange to any great extent, while other unstandard conditions may completely interrupt the service of the exchange. In the latter case, it is necessary to send out a repairman immediately to restore the service.

' F ig. 8 shows an incomine` selector ISRl terminating a two-way trun from the tandem automatic oiiice, such as the trunk terminating in selector ISR of exchange A. rThis selector is for both toll and local service. Mechanically and electricall selector ISRl is similar to selector ISR wlth certain modifications to adapt it for combination use as will be explained in later paragraphs.'

This selector has access only to connectors in the B oice.

ln Fig. 9 is shown alarm signal relay group SRI corresponding to the local alarm relays in relay group ASR, Fig. 7. The alarm signal apparatus shown is similar to that shown in Fig. 7. ln Fig. 9 are also shown the local selector Sl and connector Cl. These switches are shown only in skeleton form and are identical with the selector SR and connector C of Figs. l and 3, respectively. T3 and T4 are two ordinary automatic substations similar to sub-station T. The substation T3 terminates in line switch LS1 which is similar to line switch LS of-Fig, l.

viLocal calls in the automatic exchange are made by dialling a four digit number. For example, sub-station T in calling sub-station T2 on initiating the call is connected with a selector such as selector SR by way of line switch LS. The first digit dialled, in this case the digit tour, causes selector SR to raise. its wipers opposite the fourth level and then restore to normal. The second digit again causes the selector Slt to raise its wipers opposite the called level in which local connectors such as connector C are accessible, whereotice, in this case the digit 3, and selector SR will operate to select a trunk to the B -ofiice. The second digit of the called number will operate selector ISRl to a locallevel where a trunk extending to a local connector, such as connector C1, will be selected. The

'two final digits of the number operate connector C1 tov the contacts of the called-line which is then signalled in the usual way by the connector.

It will be noted that the two sub-stations namely Tand T1 are associated with one subscribers line. T1 isv shown to be an extension station from which calls may be extended or answered. It may in some cases' be desirable to signal between sub-stations T and T1. In this case the calling sub-station being extended to a selector, `such as selector SR, will operate this switch to the level in which the revertive ringing relay group RC 1s accessible. The selector is arranged to switch through on this level disconnecting the regular battery feeding bridges. When the receiver is hung up at the calling sub-station, the relay group RC will transmit ringing current over the callin line to ring the bellsat both the regular su -station and the extension sub-station on the line. Selector SR,

however, does not release under these conditions but is held locked up by the relay group. When either party answers, the rin is cut olf and when the receivers at the two su -stations are inally replaced, i the equipment all restores to normal in the usual way. In testing a sub-station ringer, a similar procedure is followed b the repair man.

Toll cal s for subscribers in either automatic exchange are extended manually from the toll board. A talking connection between the incoming toll line (not shown) and the toll completing trunk such as the trunk RCT of Fig. t is set up by means of the usual toll or answering cord AC. The operator then inserts the dialling cord, such as cord DC, into the dialling jack of the selected trunk and dials the last three digits of the called number if the subscriber is in exchange A, or the complete number if in the exchange B. Toll transmission selector TTS responds to the rst digit and selects a `combination connector, such as connector C in exchange A. This connector is thenoperated responsive to the last two digits to select the called line. The connector signals the called line under control of the operator at the manual board. In case the called line is busy in either a local or a toll call, the toll operator is given a distinctive signal to that effect. If busy in a local call, the operator may cut in and talk to the subscribers on'thewanted line and inform them that a toll call is waiting. In case the line wanted is not released immediately, the operator may disconnect the call in which case the toll call will be extended through tothe line. The operator cannot cut in, however, when the Wanted line is busy in a toll call. To call a subscriber inthe B oiiice, the operator dials the second exchange digit, in this case the digit 3, and toll transmission selector TTS, selects a trunk to exchange B terminating in the selector such as ISRl. The second digit operates selector ISRl to a local level and extends the call to `a combination connector such as connector C1. Connector C1 responds to the last two digits to extend the call in the same manner as connector C. Since the inter-ollice trunk is used for both toll and local calls, it is necessary that certain switching operations take place in order toprovide the proper service for the different types of calls. Such switch-over operation changing from local to toll operation is brought aboutv by a reversal of batteryover the trunk when the call is extended by Way of the toll transmission selector.

Subscribers in each exchange` may reach the toll operator over one `of thecombina-tion toll -completing and toll recording trunks by dialling a recording code such as the two digits 40, selected in this case by wav o f illustration. This code dialled from a substation in oiiice lA rst operates the first selector to a local level from which the selec- A tor drops back and cancels the digit', and in response to the lsecond digit extends the call over the O level toa trunk such as the one extending to trunk group RCT. This code dialled from a -sub-station in exchange B causes a local selector S1 to select a trunk such as the one extending to incoming selector ISR in exchange A which in turn responds to the second digit and extends the 'no call to the operator in the usual way.

Alarm signals in the 4automatic exchanges cause the operation of one of the relay groups ASR or ASBL The former relay group connects a potential to the toll recording trunk in order to signal the operator at the toll board. In the case of an alarm signal in the B oiice, the alarm relay group in that office extends the signal overan inter-office trunk to the alarm relay group in the A.

Y the equipment and the apparatus involved, a

G5 terrupter contacts 176, armature 158, winddetailed description of the vvarious connections will now be given.

@all from sub-station T to sub-station 'T2 When the subscriber at sub-station T lifts the receiver, a loop including thel impulse contacts of the calling device at sub-station T is closed for relay 5 of the associated line switch LS. This circuit extends from ground, armature 11, line conductor 3, through the calling subscribers telephone, line conductor 2, armature 8, winding of relay 5, to battery. Relay roperates, closes a circuit for relay 4 at armature 13, and at armature 12, closes the usual testing circuit by connecting the test wiper 16 between switching relay 4 and stepping magnet 6. In case the trunk on which the wipers are standing is busy, wiper 16 will encounter a groun which shunts relay 4 and causes the stepping magnet to operate andk advance the wipers to the next set of contacts. This' operation will be repeated as long as wiper 16 encounters grounded contacts. Magnet 6 opens its own circuit at interruptor contact 18 at each step. IWhen an idle trunk is found,

which will be assumed to be the` trunk terminating in selector SR, there will be no ground on the test contact engaged by wiper 16 and relay 4 being no longer shunted, will operate. The calling line loop will be extended by way oi armatures 8 and 11 and wipers 14 and 17, to the line relay of selector SR. The release trunk conductor will be `switched over from the upper to the lower terminal of relay 4 to provide a holding cir.- cuit for that relay after relay 5 releases. The metering conductor extending from wiper 15 is connected to meter 7 at armature 9.v The circuit of relay 5 is opened at armatures 8 and 11 and that relay, being slow-to-release, maintains its armatures operated long enough for the selector to return a holding ground over the release trunk to hold relay 4 operated. When the calling line is extended to the selector, a circuit is closed for line relay 101 which may be traced from battery, upper winding of relay 102, left-hand coil of relay 101, armatures 141 and 127, upper talking conductor, Wiper 14 and armature 8 of line switch LS, line conductor 2, through the loop at the calling substation, line conductor 3, armature 11 and wiper 17 of the line switch, lower talking conductor, armature 131, right-hand coil of relay 101, lower winding of relay 102, to ground. Relay 101 operates and closes a circuit from ground, armature 122, winding of relay 108, windings of relay 107, to battery, and in parallel therewith, through the ining of magnet 112 to battery. Relay 108 operates in the above circuit, but due to the high resistance of this relay, relay 107 and magnet 112 do not operate at this time. lit may be noted that relay 102 does not operate over the loop circuit traced for relay 101, be-

cause its windings are arranged to oppose each other. Relay 108 on operating, connects ground to the release trunk conductor at armature 147 to hold up relay 4 as previouslymentioned. At armature 146 an alternate circuit `is closed for relay 101 independent of armature 141. At armature 148 a short circuit for relay 108 is closed which circuit-will also serve to operate relay 107 and vertical magnet 112. Relay 101 also' closes a circuit from battery, upper winding of relay 102, upper winding of relay 103, armature 121, normally closed contacts controlled by armatures 127 and 155, respectively, upper winding of relay 106, to ground. Relays 103 and 106 operate in series over the above circuit. rlhe resistance of relay 106 is high enough so that relay 102 is not unbalanced and consequently does not operate at this time. Relay 103 upon operating opens a point in the release circuit at arma.- ture 125 and closes a point in the holding circuit of relay 106 at armature 126. Relay 106 upon operating closes a point in the temporary holding. circuit of relay 103 at armature 134, connects dial tone to the upper talking conductor of the selector at armature 135, opens a point in the busy tone circuit at armature 136, and completes its own locking circuit at armature 139. This latter circuit may be traced from ground at armature 126, armature 139, lower winding of relay 106, to battery, and serves to maintain the relay in operated position until such time as relay 103 restores. The dial tone is audible to the calling subscriber who is informed thereby that he has been connected with a first selector and that the dialling may proceed. l

1t has been assumed for the purpose of describing the operation, that the number of the called line is 4422. A calling subscriber now proceeds to dial this number by operating the calling device at the sub-station. |The calling loop is interrupted correspondingly, and relay 101 responds by reti-acting its armatures at each interruption of the circuit. At each impulse a circuit is closed from battery, upper windin g of relay 102, upper winding of relay 103, normally closed contact controlled by armature 121, armatures 150, 144, and 134, resistance 114, to ground. Relay 103 holds its armatures in operated position over the above circuits during the transmission of impulses. Resistance 114 is of such a value that the relay 102 is not unbalanced and consequently does not operate. Relay 101 by retracting its armature 122 short circuits relay 108, and a circuit is closed from ground, armature 148 contacts controlled by armature 122, through the winding of relay 107 to battery, and4 in parallel therewith;

operated. As previously stated the resistf ance of relay 108 is such that relay 107 will not operate in series therewith, nor will relay 107 remain operated when 'connected in series. This connection, however, causes thev relay 107 to become slow in releasing. Since the digit 4 was dialled, relay 101 drops back four times and transmits four impulses to magnet 112, which raises the wipers opposite the fourth level of bank contacts. On the first vertical step of the wipers, off-normal contacts 116 operate and disconnect the dial tone from the calling line, contacts 117 close a point in the releas circuit, and contacts 118 close a point in t e circuit of the rotary magnet. When the wipers reach the fourth level, shaft springs A 120 operate. These springs are adJustable and are set to operate on the particular level from which it is desired that the selector shall release.

Shortly after the last impulse of the series, relay 107 will restore. Parallel circuits are closed from ground, armatures 147, 123, 129,

.and 142, shaftisiprings 120,. armature 133,

oiinormal cohtacts 117, through release magnet 113 to battery, and byway of contacts controlled by armature 132, through the winding of relay 105 to battery. Release magnet 113 operates and the switch wipers are restored to normal position in the usual way. Relay 105 upon operating closes alocking circuit for itself at armature 132 to ground at armature 149. By actuating its armature 133, relay 105 disconnects the shaft springs from the circuit, sothat the subsequent operation of the wipers of the fourth level w1ll not affect the release of the switch. Relays 101, 103, 106, and 108 remain operated during the release of the switch.

The calling subscriber now dials the second digit of the number which is also assumed' to be the digit 4, and relay 101 responds as in the previous instance. The offnormal springs again operate on the first step and close the various circuits previously described. Relay 107 and magnet 112 operate as previously, stepping the wipers to the fourth level. Shaft springs 120 again operate but are without eiect at this time, since relay 105 is locked up, and has opened the release circuit at armature 133. Shortly after the last impulse of the series, relay 107 releases and closes a circuit from ,ground armatures 147, v123, 129, and 142, oil-norma contacts 118, armature 157, interrupter contacts 177, through the rotary magnetlll, to battery. Magnet 111 operates; and steps the wipers in on to the first set of contacts 1n the fourth level. Interrupter springs 177 operate near the end of the stroke of the ma et andA open the circuit of the magnet which restores.

Assuming that\\the first trunk of the select- Ved group is busy, the test contact engaged by wiper 161 will be grounded. The test circuit maybe traced from wiper 161, upper winding of relay 110, armatures 137 and 149, to ground. The ground encountered by wiper 161 on the busy contact, therefore, shunts the upper winding of relay 110 and consequently the relay does not operate. Rotary magnet 111, however, again closes its interruptor contacts 177 thereby completing the previously traced operating circuit of the magnet. This circuit is maintained as long as the wiper continues to engage a busy contact, the magnet 111 stepping the wipers and opening its own circuit in a buzzer-like manner.

Assume that trunk comprising conductors 163-166 is the first idle trunk or the roup. This trunk terminates in connector (Fig, 3), and when idle, is characterized by, having battery potential connected to trunk conductor 165. It may be noted that conductor 165 is used only in toll connections and is not shown connected in the banks of selector SR. .When the wipers of the selector engage the contacts associated with this trunk, wiper 161 encounters battery potential, relay 110 will operate over the previously traced test circuit and open the circuit of the rotary magnet at armature 157. The wipers of the switch are thereby stopped on the contacts of the idle trunk. Relay 110 closes a locking circuit in series with the rotary/'magnet at armature 157 The resistance of the lower winding of relay 110, however, is such thatmagnet 111 does not operate at this time. At armature'- 156, relay 110 short circuits its upper winding to prevent a possibility of interference from the switch C. At armature 158 the circuit of the vertical magnet is opened and at armatures 155 ari 159 a control circuit is extended to the connector by way of'wipers 160 and 162. It will be noted that the upper winding'of relay 104 is connected in the test circuit in parallel with the upper winding of relay 110 and subsequently directly to test wiper 161 by way of armature 156. The relay, however, is so adjusted that it does not operate in series with either the resistance 313 or the lower winding of relay 302 of connector C, when aconnection is extended. The purpose of this relay will be described in later paragraphs.

. of relay 307, armature 326, trunk conductor 164, wiper 162, armature 159, normally closed contacts controlled by armature 131, lower winding of relay 103, lower winding of relay' 102 to ground. Relay 307, which is the impulsing relay of the connector, operates over the above circuit, but relay 306 does not since `the current flow in its upper Winding is insucient to overcome the tension of the armature springs. Further'the relay is arranged so that on calls from a local selector, the two windings oppose each other as will be subsequently explained. As previously mentioned, the relay 110 upon operating short circuits its upper winding and connects ground to the release trunk through the low-resistance upper Winding of relay 104. rlhis ground extending by way of wiper 161, conductor 165, armature 333, off-normal contacts 315, lower winding. of relay 302, resistance 312 to battery, causes the operation of relay 302. Relayl 302 locks itself to the release trunk at armature 331, thereby rendering itself independent o off-normal contacts 315. Relay 302 opens a point in the release circuit at armature 329, and at armature 330 connects a ground to local holding conductor 320 the purpose of which will be apparent from the later description. Relay 307 operates as previously mentioned and vprepares the impulsing circuit at armature 355. The purpose of the parallel battery connection through resistance 313, which is a non-inductive resistance, is to increase the battery flow in the test circuit to insure the quick operation of the switchingr relay of the selector. l

The calling subscriber now proceeds to dial the third digit of the called number which is assumed to be the digit 2. Relay 101 of selector SR responds as in the previous instance and opens the control circuit of relay 307 at armature 121. Relay 307 responds to the impulses and on restoring at each impulse, closes a circuit from ground, armature 330, contacts controlled by armature 355, armatures 325 and 344, thence in two parallel circuits one extending through relay 304 to baty tery, the other by way of armature 335 through vertical magnet 308 to battery. Re-

lay 304 which is a slow acting relay, operates in response to the irst impulse and remains operated throughout the series of impulses. Magnet 308 operates in response to each impulse and raises the wipers of the switch opposite the called level, in this case since two impulseswere transmitted the Wip- Leonesa ers are raised opposite the ysecond level of the bank contacts. Relay 304 upon operating closes a point in the trunk circuit at arma:- ture 337 shunting the armature 341, and opens a point in the circuit of relay 303 at armature 339. Upon the first vertical step to the wipers, od-normal contacts 315, 316, and 317 are operated, the former opening the circuit of relay 302 which, however, remains locked by way of armature 331 and the release trunk conductor; contacts 316 close a circuit for grounding conductor 320 to be effective after the release ot relay 302; and contacts 317 close a point in the circuit of the upper winding ot relay 301 and of switch-over relay 303. Shortly after the last impulse of the series, relay 304 restores and closes a circuit from ground, armatures 330 land 355, oil-normal contacts 317 closed on the first vertical step, armatures 343 and 339, through the winding of relay 303 to battery. A parallel circuit is closed through the resistance 314, lower winding ot' relay 306 to battery. Relay 303 operates and locks itself to the release trunk conductor at armature 333 and opens the circuit vof relay 302. A point in the circuit of the release magnet is opened at armature 334, and ground. by way of off-normal contacts 316 is connectedto local holding conductor 320. The impulsing circuit is now switched from vertical magnet 308 to rotary magnet 309 at armature 335- Relay 306 does not operate over the previously traced circuit due to the value of resistance 314. Relay 302 now releases and prepares the ringing and release circuit.

The calling subscriber now dials the final digit of the number, that is the digit 2, and

relays 101 and 307`respond as in the previous instance. Relay 307 transmits two impulses to rotary magnet 309 which operates to step the wipers around to the contacts of the called line. Relay 304 again operates and remains operated during the series of impulses. At armature 337 4 the circuit of relay 307 is maintained and at armature 340 the impulsing circuit is maintained independent of the contacts of relay 305 in order to prevent that relay from interfer'ring with the operation of the switch as the wipers pass over busy contacts. Test relay 305 is connected to test wiper' 357 at armature 338. lt will be assumed that the called line is the one comprising the conductors 359-361 terminating in sub-station T2. I' the called line is busy there will be a ground on the test contact engaged by wiper 357. Relay 305 operates from this ground, and prepares a locking circuit Jfor itseli1 at armature 342. A. point in the circuit of relay 307 is opened at armature 341 and points in the circuit of the upper winding of relay 301 are opened at armatures 343 and 345. The impulsing circuit is lopened at armature 344, and the busytone is connected upl at armature 347. Shortly after the last and also the impulsing circuit at armature 340. Relay 305 is disconnected from the test wiper and now remains locked up by way of contacts controlledby armature 338, arma-- tures 342,323, and 334, and off-normal contacts 316 to ground. Relay 307 releases but is without effect at this time.

Returning now to selector SR, the opening of the control loop at the connector 'causes relay 103 to release and open the holding circuit of relay 106 at armature 126. Relay 106 releases and switches the selector over from operating to talking position by switching the talking circuit from wiper 160 through to condenser 178 at armature 135. Relay 104 is shunted out at armature 137 to prevent the subsequent operation of this relay. The busy tone from the connector is now transmitted to the calling subscriber by way of condenser 179 and the lower trunk conductor. The calling subscriberis thereby informed that tho called line is engaged and the subscriber is expected to hang up4 and release the connection.

In case the called line is idle when the wipers of the connector are operated into engagement with the contacts of thefline, wiper 357 will not encounter ground. consequently, relay 305 does not operate. lVhen'relay 304 releases shortly after thelast impulse of the series, relay 301 operates over a circuit from ground, o -normal contacts 316, armatures 334 and 355, off-normal contacts 317, arma ture 343, upper winding of rela 301, armatures 345, 354, and 338, wiper 35 trunkvconductor 360 through the eut-oil' relay and magnet of the associated line switch corresponding respectively to relay 4 and magnet 6 of line switch LS, to battery. Relay 301 closes a locking circuit for its lower winding at armature 324 in series with `vertical .magnet 308. Magnet 308, however, does not operate due to the high resistance of relay 301. The ringing circuit is closed through to the called line at armatures 320 and 327 land at armature 321 a ring back circuit for the calling line is closed by way of condenser 319. The control circuit of relay 307 is opened at armatures 321 and 326 and relay 307 restores. Ground from armature 350 is connected directly to the test wiper 357 by way of armature 322 to mark the line locally busy. Relay 301 by operating its armature 325 also prepares a locking circuit for the ring cut-olf relay 302. At the selector SR, the switch-over operation takes place as was previously explained when a busy line was connected.

The connector now sends out interrupted ringing current over the called line from grounded generator Gen, upper winding of relay 302, armatures 328 and 320, wiper 356, line conductor 359, through the bells at the called sub-station T2, line conductor 361,

wiper 358, armatures 327 .and 332, to battery. I

AThe ringing current is interrupted in the connected to local holding conductor 320 at armature 330. Relay -302 also closes a locking circuit for itself which may be traced from ground at armature 330 or olf-normal contact 316, conductor 320, contacts controlled by armature 355, (relay 307 having restored) armatures 325 and 331, lower winding of relay 302, resistance 312 to battery. In the selec'tor,.relay 103 now/operates over the called line loop, the previously traced control circuit for relay 307 having been-extended by way of the wipers through to the called line. The two subscribers may now talk, battery for the calling subscriber being supplied throughy line relay 101, and for the called subscriber through relay-103. The calling and called loops are inductively connected through the condensers 178 and 179.

Relay 103 as previously mentioned operates when the called subscriber answers. A circuit is closed from ground by Way of armatures 126, 139, and 143 through relay 109 to battery. Relay 109 operates and locks to ground at armature 149 by way of armature 153. Relay 109 remains operated during the conversation and closes a point in the talkin g circuit at armature 150, opens a point in the release circuit at armature 151, and prepares the metering circuit at that armature.

When the subscribers finish talking, the receivers at both the calling and the called sub-stations will be restored. lVlien the called party hangs up, the circuit of relay 103,

which has been feeding the talking battery to the called party, will be opened and thatA relay will restore. The calling party upon hanging up opens-the circuit of line relay 101 and that relay will restore. A circuit may nowfbe traced'` from ground, armature 148, contacts controlled by armature 122, through relay 107 to battery. Relay 107 operates, 4and at armature 142 connects ground to the release trunk by way of armatures 129 and' 123, to holdup the cut-off relay 4 of line switch LS and to maintain the holding circuit for switching relay 110 of the selecto-r. The circuit of relay 107 will be-maintaincd a. short time after relay 101 releases due to the slow-releasing characteristic of relay 108. Relay 107 is rendered slow-to-release at this time by the shortl circuit of its lower winding through armatures 138 and 158 and interrupter contacts 176. Shortly after the release of relay 101, relay 108 will fall back and close the metering circuit which may be vtraced from ground, meter 7 associated with line switch LS, armature 9, wiper 15, metering-conductor, armatures 151, 145, 125, and 128, oli-normal contacts 117, through the winding of magnet 113, to battery. Meter 7 operates over the above circuits and registers the call; the magnet 113, however, does not operate due to the relatively high resistance of the meter relay. Relay 107 remains operated for a time after relay 108 lfalls back and maintains the'holding ground on the release trunk. The release of relay 108 also opens the circuit of relay 109 which vbeing slow acting, maintains its armatures actuated for` a short time after its circuit 1s opened, to eect the just described metering lfunction. After a slight delay, relay 109 restores and closes the release circuit at armature 151, opening the metering circuit at the same time. Release magnet 113 operates to restore' the switch wipers to normal position, and at contacts 180, closes a holding circuit for relay 107 to keep that relay operated until the connector has reached the normal position. When the wipers return, to the normal position, the oli-normal contacts are again operated and the circuit of the release magnet is opened at oil-normal contacts 117. Release magnet then restores, opens the circuit of relay 107 which likewise restores its armatures, and removes ground from the release 'trunk thereby permitting the switching relay 4 of the line switch and switching relay 110 of the selector to restore. The release of relay 108 removes the holding ground from test wiper 161 and release trunk conductor 165, thereby permitting relay 303 of connector C to restore. Relay 303 disconnects the lower winding of relay 301 from magnet 308 and connects it instead to the upper talking conductor of the connector at armature 336 and contacts controlled thereby. If the called subscriber has hung up, relay 301 releases after a. short interval and opens the holding circuit of relay 302 at armature 325. Relay 302 releases and at armature329 completes a circuit for release magnet 310 which restores the switch wipers to normal position in the usual way. The switches are thus all restored to their normal positions and are available for. another call.

In case the called subscriber fails to hang up after a call, the various switches except connector C release as above described. After the release'of relay 303 which occurs in retenaces lower winding of the relay, armature 324, contacts controlled by-armature 336, armatures 328 and 320, wiper 356, called line loop,

wiper 358, armatures 327, 332, 326, 336, wind.

ing ont magnet 308, to battery. Relay 301 will remain operated over this circuit until the called subscriber hangs up and will, of course,

Reeerz'vc @all from sub-station T to extension aub-station T1 As previously explained, T and T1 are two sub-stations on the same subscribers line, T1 being what is ordinarily known as an extension telephone. Both sub-stations are equipped with the usual calling devices and ringers. Assuming that the subscriber at sub-station T desires to talk with the subscriber at sub-station T1, the subscriber at sub-station T will remove the receiver from the hook and line switch LS will operate in the manner previously described to extend the calling loop to a selector such as selector SR. A particular level in the banks of the selectors is set aside for revertive ringing, for example, the ninth level. A calling subscriber, therefore, dials only the digit 9 to complete the call.

When the call is extended to a selector which will be assumed to be the selector SR, relays 101, 103, 106, and 108 operate as previously described. Relay 101 responds to the interruptions from the calling device at sub-station T and transmits a series 'of impulses, in this case 9 impulses, to vertical magnet 112 which operates and sets the Wipers opposite the ninth level exactly as in the previous connection. Relay 107 operates during the series of impulses as in the previous connection. Shortly after the last impulse of the series, relay 107 releases and completes the usual rotary circuit. The wipers of the selector are then automatically advanced step by step until an idle 'trunk is` reached. Assuming that the first idle trunk is the one comprising conductors 167-169, the wipers of the selector advance to the contacts associated withthis line. Switching relay 110 ofthe selector operates over the usual testing circuit of the selector and by way of wiper 161, trunk conductor 168, contacts controlled by armature 226 of relay group RC, resistance 209, relay 207., to bat tery. Relay 207 of the relay group does not operate in this circuit, due to the value of resistance 209. Relay 110 upon operating extends the control loop of selector SR through to relay group RC, a circuit extending from battery, upper windings of relays -102 and 103, armature 121, contacts controlled by armature 127, armature 155, wiper 160, trunk conductor 169, armature 220, upper winding of relay 201, armature 228, lower winding of relay 201, armature 222, trunk conduct-or 167, wiper 162, armature 159, contacts controlled by armature 131, lower windings ot'- relays 103 and 102, to ground. Relays 103 and 106, which were operated in a local circuit previous to the switch through of the selector, are now held up over the loop circuit through relay group RC. Relay l1()` short circuits its upper winding at armature 156 and relay 106 removes the. short circuit from the upper winding of relay 104 as in the previous connection. Relay 201 of the relay group now operates over the control loop, closes a circuiti for relay 202 at armature 212, prepares a holding circuit for relay 203 at armature 211, and at armature. 210 short circuits resistance 209 in the release trunk circuit. The increased current flow in this circuit now causes relay 104 ot selector SR and relay 207 of relay group RC to operate in series. Relay 104 upon operating connects the calling loop straight through to wipers 160 and 162 by way of armatures 127 and 131, and opens the circuit of impulsing relay 101 at those` armatures. Relay 104 opens a point in the release circuit at armature 128, connects the upper and lower windings of relay 110 in series at armature 129, and at armature 130 closes a locking circuit for its own lower win-ding in parallel with the holding circuit of rela-y 110. Relay 101 now restores followed by the restoration of relays 103, 106 and 108. Relay 207 on operating, connects the lower winding of relay 206 to the release trunk by way of armature 230. Relay 206 now operates and relays 110 and 104 are held up over a circuit extending from ground, lower winding of relay 206, armature 230, conductor 168, wiper 161, armatures 156, 129, and 123, lower winding of relay 110, armature 157, interrupter contacts 177, through rotary magnet 111 to battery. The. circuit of relay 104 includes armature 130. Relay 206 upon operating closes a locking circuit-for itself at armature 227 by way of armature 214 and at varmature 226 connects a direct ground to the release trunk vto hold up relays 110 and 104 of selector SR over the previously traced circuit.

Relay 207 is now disconnected from the release trunk and that relay releases Iand opens the original energizing circuit of relay 206 of armature 230. Relay 206, however, remains locked up and connects battery and ground, respectively, to the upper and lower winding of relay 201, which is now held operated over the calling loop. Relay 202 on operating as previously mentioned, closed a locking circuit for itself at armature 215 and including armature 218, prepared a cir- `may take place.

cuit for grounding the release trunk at armature 214, and at armature 216 prepared an operating circuit for relay 204.

The calling subscriber now restores 'the .receiver to the switch hook, opening the calling loop, and relay 201 releases. The original energizing circuit of relay 202 is opened at armature 212, and a circuit is closed to relay 204 which may be traced from ground at armatures 216, 213, and 219, winding of relay 204, to battery. Relay 204 operates and at armatures 220 and 222 closes the ringing circuit, and closes the circuit for relay 205 at armature 221. Relay 205 operates, closes points in the holding circuit of relay 203 at armatures 223 and 224, and at armature 225 completes a locking circuit for itself to ground on the release trunk. Ringing current or ground is now'intermittently Connected to the calling line over a circuit which extends from grounded generator GEN or ground by way of armature 231 of interrupter relay INT, lower winding of relay 203, armature 220, conductor 169, wiper 160, armatures 155 and 127, upper talking conductor of the selector, wiper 14,01? the line switch LS, armature 8, line conductor 2,

The bells at both sub-stations will ring intermittently until a receiveris lifted at one substation or the other. Assuming that the called party, that is the subscriber at substation Tl, answers first, a direct current circuitk is closed for relay 203 and that relay operates and closes a locking circuit for itself at armatuure 217 t'o ground on the release trunk by way of armatures 224 and 226. Relay 203 opens the locking circuit of relay 202 at armature 218, and at armature 219 opens the circuit of relay 204. Relay 204 now restores and opens the ringing circuit at armatures 220 and 222 and again connects relay-201 to the calling loop. Relay 201 operates, closes the circuit of rela 202 before that relay has had time to fall ack, and at armature 211 closes an additional locking circuit for relay 203.

The calling subscriber on noting that the ringing has ceased, knows that the called subscriber has answered and, therefore, will again lift his receiver and the conversation Talking battery for both subscribers is furnished through the winding of relay 201.

Wheny the conversation is finished, both parties will restore their receivers, thus opening the circuit of relay 201 which releases, opens the circuit of relay 202 and the addi- "tional locking circuit of relay 203.4 Relay to battery. The release magnet operates to restore the wipers to normal position, and at contact 180 closes an energizing circuit to relay 107. Relay 10.7 operates, at armature 142, connects ground to the release trunk to guard the selector against seizure until the wipers have reached normal position. On

reaching normal position, the off-normal contacts are operated and the circuit of the release magnety is opened at contact 117. Relay 107 now releases and removes the guarding ground from the release trunk and the apparatus is again in condition for another call.

Call from Vsu?).fnfatzo'n T to sub-station T3 When the receiver is lifted at sub-station T, line switch LS operates as previously described to extend the calling line to a selector. Assuming that the selector SR is the one taken into use, relays 101, 103, 106, and 108 operate as previously described in a local connection. The sub-station T3 is assumed to be in oiiice B to which the digit has been assigned as an oiiice code. For purpose of illustration it may be assumed that the directory number of this sub-station is 3322. The calling subscriber now dials the first digit, that is the digit 3, and the wipers of selector SR are raised to the third level exactly as was done in a local call. Shaft springs 120, however, are not operated on this level and, consequently, relay 105 does not operate to release the selector and cancel the irst digit. Shortly after the last impulse of the series, relay 107 releases and closes the previously traced rotary and testing circuits by means of which the selector now selects an idle trunk. The trunk selected, for exam ple, may be the one comprising conductors 17 3-17 5 terminating in selector ISR at exchange A and in selector ISRl at exchange B. It may be noted that signal relays ASR and ASRl have associated with the trunk at oiiices A and B, respectively.

The test circuit including the upper winding of relay 110 extends by way of wiper 161, conductor 174, contacts controlled by armature 746, (Fig. 7) through the winding of relay 712, to battery. Relay 110 loperates to switch through the control loop, closes its own locking circuit and opens the circuit of the vertical magnet as was described in the previous connection. Relay 712 of the alarm signal relays also operates and closes a circuit for relay 711 at armature 750. Relay 711 operates and closes an alternate holding circuit for relay 712 by wa of armatures 746 and 749. A circuit is also closed from ground, armature 748, conductor 174', thence through armature 625, windin 'of relay 601 of the incoming selector ISR ig. 6), to battery. Relay 601 operates and at armatures 621 and 623 disconnects the selector llSR from the trunk. The control loop of selector SR which includes the two windings of relay 103, is now extended by way of wipers 160 and 162, trunk conductors 173 and 175, armatures 833 and 835 of incoming selector ISRl (Fig. 8), through the left-hand windings of the re eatin coil R, contacts controlled respectlvely y armatures 840 and 841, and through the upperwindings of relays 802 and 805 in series. Relay 802, which is the impulsing relay, operates in the above traced circuit, but relay 805 does not since the current flow in its upper winding is insufficient to actuate the armatures.` Relay 802 upon operating closes a circuit from ground, armature 888, winding of relay 803,v thence through relay 810 to battery, and in parallel therewith through vertical magnet 817 to battery by way of armature 878. Re-

lay 803 operates in the circuit but relay 810 and the vertical magnet do not operate due to the high resistance of relay 803. Relay 803 upon operating, grounds the local holding conductor at armature 837, disconnects cutolf relay 801 at armature 836, and opens a point in the release circuit at 838. The grounding ofthe local holding conductor completes a circuit for the lower winding of relay 805 in series with resistance 822. Relay 805, however, does not operate at this time due to the value of resistance 822 and due to the fact that the two 'windings now oppose each other. Impulsing relay.v 802 upon operating also closes a circuit from battery through the lower windings of relays 808 and 807, armatures 889, 891, and 844, lower righthand winding of repeating coil R, contacts controlled by armature 879, resistance 890, to ground. Relay 807 operates over this circuit, but relay 808 does not operate due to the resistance 890. y

The subscriber now dials the second digit of the called number, in this case the digit 3, and relay 101 responds to the interruption of the calllng loop as in the previously describedconnection. The circuit of the control loop is intermittently opened at armature` 121, and relay 802 responds to these interruptions by retracting its armatures three times. Each time relay 802 drops back, a circuit is closed from ground, armature 837, contacts controlled by armature 888, through the'winding of relay 810 to battery, and in parallel therewithby wayof armature 878, through vertical magnet 817, to battery. Magnet 817 responds to these impulses and raises the wipers of the switch three steps to the third level. Relay 810 also operates in response to the impulses and due to its slow releasing characteristics remains operated throu' hout the series of impulses. This slow releaslng action of relay 810 is due-to its series connection with relay 803 when relay 802 is in operated condition. Relay 803 also remains operated during the impulsing as 1ts winding is short' circuited at contacts controlled by armature 888, which renders the relay slow acting. Each time relay 802 drops back to transmit an impulse, a holding circuit for relay 807 is closed which may be traced from battery, lower windings of relays 808 and 807, contacts controlled by armature 889, resistance 821, armature 843, to ground on the local holding conductor at armature 837.

Y Relay 808 is prevented from operating at this time by resistance 821. After the last impulse-in the series, relay 810 releases, closes a circuit from ground on the local holding conductor, oil-normal contacts 827 which closed on the first vertical step of the wipers, release magnet contact 831, armatures 858 and 877, interruptor springs 832, through the winding of rotary magnet 818, to battery. Magnet 818 operates and steps the wipers in on the contacts of the first trunk inthe selected level and near the end of its stroke opens its own circuit at interrupter contacts 832. The magnet then releases and again closes its circuit at interrupter contacts 832 and unless the rotary circuit has been opened at some other point, yanother rotary step is imparted to the wipers. This action takes place until an idle trunk is encountered which may be assumed to be the trunk comprising conductors 931934 terminating in connector C1, Fig. 9. 4

The idle trunk is marked by the presence of battery potential on the test contact by way of the ring cut-oli' relay of the connector C1 (corresponding to relay 302 of connector C). Relay 815 now operates from the battery encountered by wiper 885, armature 852, upper winding of relay 815, and ground on the local holding conductor. Relay 815 upon operating switches the control loop including the lower winding of relay 807 through to the line relay of the connector Cl. The line relay of connector C1 corresponds to the relay 807 of connector C previously described. The control circuit extends from battery, lower windings of relays 808 and 807 in series, armatures 889,891, and 844, lower right-hand winding of repeating coil R, armatures 879 and 882, wiper 886, trunk conductor 932, through the line relay of connector C1 (corresponding to relay 307 of connector C), trunk conductor 934, wiper 883, armatures 880, 875, and 867, upper right-hand winding of repeating coil R, armature 842, to ground. Relay 807 remains operated now over` the above traced loop circuit. Relay 808 does not operate at this time due to the resista-nce of the loop circuit. It will be noted that the two right-hand windings of repeating coil R aire connected by way of armature 854 and condenser 893.

The subscriber now dials the last two digits of the called number and relays 101 and 802 respondy as in the previous instance. lRelay 802 interrupts the control loop extendingY to connector C1 at armature 889 and completes the holding circuit for relay 807 during impulsing as previously explanied. Connector C1 vresponds to the two digits in the same manner as explained for connector C and advances wipers 356 -358 into engagement with the contacts of the. called line, for eX? ample, the line comprising conductors 2', 3, and 20. Relay 810 again operates during opens a connection between the right-hand Winding of the repeating coil R.

If the called line is busy, wiper 357 encounters a grounded contact and the busy relay of the connector will operate to open the control loop and to connect the busy tone to the trunk. When the control loop is opened, relay 807 deenergizes and at armature 851 closes a circuit for relay 804. Relay 804 operates and at armature 843 locks itself to the local holding conductor. The windings of relays 802 and 805 are now disconnected from the control loop extending from selector SR, and relays 806 and 809 are each series of impulses and at armature 854 i connected, respectively, to the trunk -conduc- -l tors -173 and 175. Relay 806 now operates in series with the lower windings of vrelays 103 and 102 of selector SR, but due to the very high vresistance of relay 806, relay 103 retracts its armatures. Relay 806 also closes a holding circuit for impulsing relay 802, from ground, armature 849, lower winding of relay 802, to battery. The busy tone from the connector is now induced on the trunk line by way of the repeating coil R, and is audible to the calling subscriber who is thus informed vthat the calling line is engaged. The calling subscriber is expected to hang up and release the connection.

Incase the line connected with is idle, connector C1 switches through in the usual way, and cut-off relay 4 of line switch LS1 associated with the called line operates, discon- 1 necting battery and ground from the line.

The connector switches through and opens the control loo as previously explained in the operation o .connector C. Relay 807 releases and relay 804 operates exactly as described for a call to a busy line.

The release of relay 103 and selector SR initiates the switch-over operation in that selectoras previously described, that is the switch is changed over from operating to talking con-` dition by the release of relay 106. The connector signals the called subscriber in the lusual way by 4transmitting ringing current over the line conductors. When the'called subscriber answers, the connector .cuts oil' the 

